1. Field of the Invention
The present invention relates to a process for manufacturing tea beverages, suitable for the tea beverages filled in containers that sediments do not occur even during the long-term storage. It particularly relates to a process that can prevent from the occurrence of secondary sediment predicting the occurrence of the secondary sediment.
2. Related Art Statement
In these days, green tea beverages tightly filled in cans or plastic bottles have been continuously developed. During the storage, green tea beverages have something flocky, floating, or white turbidly suspended matter, or precipitate, that is, xe2x80x9csedimentxe2x80x9d occurs, and this is a problem for the beverages. When such sediment occurs, especially, in the case of green tea beverages filled in clear bottles, the marketability will be lost due visual impressions.
The said sediment can be classified into xe2x80x9cprimary sedimentxe2x80x9d and xe2x80x9csecondary,xe2x80x9d where the primary sediment occurs immediately after the production of tea beverages, while the secondary sediment occurs gradually with time during the storage of the products. The primary sediment obviously occurs where caffeine bind with tannin or protein. It has been confirmed, as a preventing method, that the occurrence of the primary sediment can be surely prevented by kieselguhr filtration or membrane filtration after centrifugal separation of a tea extract.
Although there are various views for the secondary sediment, there has been no established view on the occurring mechanisms. As one of the main views, the following has been known that xe2x80x9cwhen green tea leaves are extracted, the extract contains a high concentration of flavonol in the un-oxidized state at first. The flavonol, particularly, a catechin component, is gradually oxidized with metal ions, such as calcium, magnesium, aluminum, zinc or iron, and dissolved oxygen in the extract to become macromolecular polyphenol. Such oxidized polyphenol gradually binds with caffeine, proteins, pectin or polysaccharides by the catalytic action of metal ions to form complexes. As the complexes are formed, green tea beverage turns the color from clear light green to brown, the suspended matter gradually begins to occur, and then, the visible flock secondary sediment is formed.xe2x80x9d
The conventional manufacturing processes of tea beverages to prevent the occurrence of secondary sediment are mainly the following 4 methods:
a) Removing the cause substances of the sediment by filtration, such as ultrafiltration, microfiltration or kieselguhr filtration;
b) In the process a), before the filtration, adding ascorbic acid and sodium bicarbonate, or actively precipitate the cause substances of the sediment by rapid cooling, followed by filtration;
c) Adding chemicals or enzyme reagents to solubilize or stabilize the insoluble complexes; and
d) Adsorbing and removing metal ions in a tea extract by ion exchange treatment.
As the method a), for example, Japanese unexamined patent publication No. 63-036745 discloses a treatment of a tea extract by adjusting a tea extract at 5-15xc2x0 C. with an ultrafiltration membrane (molecular weight of 10,000-100,000), and removing the tea cream. Also, Japanese unexamined patent publication No. 04-045744 discloses a manufacturing process of clear green tea beverages by fractionating water-soluble tea components obtained by extracting green tea leaves, fresh or dry tea leaves by ultrafiltration, and removing macromolecular components having a molecular weight of 10,000 or more.
As the method b), for example, Japanese examined patent publication No. 07-097965 discloses a method to clarify beverages by adding ascorbic acid to a green tea extract to acidify, cooling rapidly, centrifuging, and then, filtrating with kieselguhr. Japanese unexamined patent publication No. 06-269246 discloses a method to clarify beverages by extracting a green tea with warm water, cooling the obtained extract, adding tannic acid to the extract, standing still, removing fine tea particulates by centrifuging, and then, filtrating with kieselguhr. Japanese unexamined patent publication No. 11-056241 discloses a manufacturing process of tea beverages by adding sodium ascorbate to a extract obtained by extracting tea leaves, followed by cross-flow system with microfiltration membranes. Japanese unexamined patent publication No. 06-311847 discloses a method for preventing from the precipitation of the sediment by adding chitosan to a water-soluble component of green tea, adsorbing macromolecular polyphenol, adsorbing and recovering the adsorbed chitosan and the residual chitosan with kieselguhr.
As the method c), for example, Japanese unexamined patent publication No. 08-228684 discloses a method to effectively inhibit the occurrence of secondary sediment of green tea beverages, by centrifuging or cloth-filtering the warm-water extract of green tea, further combining with a process adding an enzyme having a hemi-cellulose activity. Japanese unexamined patent publication No. 2001-045973 discloses a method to inhibit the occurrence of flock in beverages, by adding xcex1-amylase to a green tea extract. Also, U.S. Pat. No. 4,501,261 (Jongeling) can be referred to as the method c).
As the method d), Japanese Patent No. 3,152,416 discloses a method for producing tea, by treating with a cation exchange resin having a sulfonic acid group previously bonded with potassium ion.
The main methods among the conventional manufacturing process of tea beverages have been tried and tested. Although all the methods have their own effects, many of the methods highly depend on the raw materials used. When the beverage concentration is increased more than those of the examples, in the balance with the flavor, there have been the cases that the secondary sediment occurred.
In order to test whether the secondary sediment occurs in produced tea beverages, generally, store the products at room temperature or under the warming condition for a long term, such as, for about 6 months, and continuously observe the occurrence. Once the occurrence of the secondary sediment is observed, a great deal of labor and time have been required since the reselection of the raw materials and respecification of the production condition have to be determined to retest.
The studies on the causes of the secondary sediment forms during the long-term storage of green tea beverages are carried out. From the studies, the inventors found that xe2x80x9cstrictininxe2x80x9d in a tea extract or formulation is one of the cause substances for the occurrence of secondary sediment. The strictinin is decomposed to ellagic acid during a process of heat-sterilization, and the said ellagic acid binds with protein to form the secondary sediment. The present invention is characterized in that the manufacturing process of tea beverages carrying out with a process determining the strictinin content in a tea extract or formulation during the process.
The strictinin is a compound (1-O-galloyl-4,6-O-(S)-hexahydroxydiphenoyl-xcex2-D-glucose) shown by the following chemical formula 1, and is one of tannins, particularly, ellagitannins extracted from tea. (xe2x80x9cCasuariin, Stachyurin and Strictinin, New Ellagitannins from Casuarina Stricta and Stachyurus Praecoxxe2x80x9d, Chem. Pharm. Bull. 30 (2) pp. 766-769, 1982). 